AN INVESTIGATION OF LOCAL ALPINE TERRESTRIAL TEMPERATURE LAPSE RATES IN THE CANADIAN ROCKIES

A common problem in alpine climatological and meteorological investigations is the lack of high spatial resolution meteorological records over the area of study. This need is demonstrated by studies ranging from Laurentide Ice Sheet modelling to alpine glacier energy balance models. Frequently in North America the available data is that from national climate station networks (such as Environment Canada and National Weather Service) whose spacing is of the order of 50 km or more, and are often located in urban areas rather than the remote alpine environs under study. For paleoclimatological work the situation is even more dire as temperature data is only available from widely spaced Global Climate Model (GCM) output or from geological proxies. For work where resolution greater than ca. 50 km is desired, temperature data must be extrapolated across the landscape using lapse rates.

Such extrapolations require an understanding of the vertical temperature lapse rate for the region, and commonly a value in the range of 5.5 °C km -1 to 6.5 °C km –1 is applied and assumed constant for a multitude of landscapes and climate regions. This range of values is derived from conditions measured in the free atmosphere where temperatures are much less affected by surface radiative transfer, frictional properties and diurnally evolving temperature structures. On the surface, where the lapse rate is applied, these influences are important to the measured temperature. One study done to account for this inconsistency determined lapse rates using surface temperature data taken from National Weather Service climate stations, however, this data was too wide spread to provide lapse rates for mountainous regions on the scale of individual valleys and ridges as are often needed.

To help begin to fill this void we have made measurements of temperature along both glaciated and deglaciated alpine valleys in the Rocky Mountains, Canada. HOBO and Veriteq temperature data loggers were placed at 100m vertical intervals along three separate valleys including one transect that reached from valley mouth to glacier headwall. Temperature was recorded at 10 minute intervals to capture short as well as long term fluctuations at each sampling site. Presented here are the lapse rates derived from the initial 3 months of this data. We show that temperature depends strongly on underlying surface types and changes in local diurnal temperature structure. Based on the data presented here, we feel that application of a uniform lapse rate across large areas is not appropriate.